Actuator device and liquid-jet head

ABSTRACT

An actuator device includes a plurality of piezoelectric elements formed on a surface of a substrate. Each piezoelectric element is configured of a piezoelectric layer, an upper electrode, and a lower electrode that is formed across the plurality of piezoelectric elements. The actuator device also includes a thin film portion provided to a region in the lower electrode between each adjacent two of the piezoelectric elements. The thin film portion has a thickness smaller than that of a region in the lower electrode provided to each piezoelectric element. The actuator device also includes a concave portion provided to the boundary portion between each thin film portion and the piezoelectric element adjacent thereto. In the actuator device, the inner surface and an edge of the opening, which is opposite to the adjacent piezoelectric element, of the concave portion are formed into curved surfaces.

The entire disclosure of Japanese Patent Application No. 2006-159027filed Jun. 7, 2006 is expressly incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to an actuator device includingpiezoelectric elements displaceably provided on a substrate, and to aliquid-jet head using the actuator device.

2. Related Art

An actuator device including piezoelectric elements, each of which isdisplaced by application of a voltage, is used as, for example, aliquid-ejecting unit for a liquid-jet head mounted on a liquid-jetapparatus, which jets a liquid droplet. As such a liquid-jet head, forexample, the following type of ink-jet recording head has been known. Inthe type of ink-jet recording head, a part of a pressure-generatingchamber communicating with a nozzle orifice is formed of a vibrationplate, which is deformed with the piezoelectric element. With thedeformation, ink in the pressure-generating chamber is pressurized, andthus ink droplets are ejected from the nozzle orifice.

As an ink-jet recording head of this type, the following one has beenproposed. Specifically, in the ink-jet recording head, a lower electrodeis provided along a direction of the shorter sides of a plurality ofpiezoelectric elements. Then, lower electrode removed portions areprovided by removing a region in the lower electrode between eachadjacent two of the piezoelectric elements so as to have a thicknesssmaller than that of a region where each piezoelectric element is formed(for example, refer to p. 14 and FIG. 16 of JP-A-2005-94688).

In another ink-jet recording head that has also been proposed has alower electrode removed portion provided on each side of thepiezoelectric elements in the width direction of each piezoelectricelement. In each lower electrode removed portion, a part of a lowerelectrode is partially removed so as to be formed into a thin film (forexample, refer to p. 16 and FIG. 6 of JP-A-11-151815).

The configuration with lower electrode removed portions, such as onesdisclosed in JP-A-2005-94688 and JP-A-11-151815, has the followingadvantage that the displacement characteristics of the vibration plateare improved, which results in an improvement in the displacementcharacteristics of each piezoelectric element. As a result, theink-ejecting characteristics are improved. The above configuration,however, has a problem. Specifically, in the above configurations,stresses are concentrated on portions, such as a corner defined by thelower electrode removed portions. As a result, the drive durability isdeteriorated.

Moreover, in a case where a protective film having moisture resistanceis provided to the piezoelectric elements, another problem occurs.Specifically, when the protective film is formed, a surface unevennessor the like occurs in the protective film due to a corner defined by thelower electrode removed portion. As a result, the part of the protectivefilm where the surface unevenness occurs is cracked by the drive of thepiezoelectric elements.

SUMMARY

Accordingly, an advantage of some aspects of the invention is to providean actuator device, in which the liquid-ejecting characteristics areimproved while drive durability is maintained, and to provide aliquid-jet head using the actuator device.

A first aspect of the invention for solving the above described problemsprovides an actuator device with the following characteristics. Theactuator device includes a plurality of piezoelectric elements formed ona surface of a substrate. Each piezoelectric element is configured of alower electrode, a piezoelectric layer and an upper electrode. The lowerelectrode is formed across the plurality of piezoelectric elements. Theactuator device also includes a thin film portion provided to a regionin the lower electrode between each adjacent two of the piezoelectricelements. The thin film portion has a thickness smaller than that of aregion in the lower electrode provided to each piezoelectric element. Inaddition, the actuator device includes a concave portion provided to theboundary portion between each thin film portion and each of adjacent twoof the piezoelectric elements to the thin film portion. In the concaveportion, the inner surface and an edge of the opening, which is oppositeto the adjacent piezoelectric element, are formed into curved surfaces.

According to the first aspect, the thin film portion and the concaveportion are provided to the lower electrode. This results in animprovement in the displacement characteristics of the piezoelectricelements. Meanwhile the rigidity of the lower electrode is maintained sothat the drive durability of the lower electrode is also maintained. Inaddition, the curved inner surface and the curved edge of the opening ofthe concave portion contribute to an improvement in the rigidity of eachconcave portion, resulting in a more reliable achievement of improvementin drive durability.

A second aspect of the invention provides the actuator device accordingto the first aspect with the thin film portion and the concave portionprovided along the longitudinal direction of each piezoelectric element.

According to the second aspect, it is possible to improve thedisplacement characteristics of the piezoelectric elements while thedrive durability of the lower electrode is maintained.

A third aspect of the invention provides the actuator device accordingto the first or second aspect with a protective film formed of aninsulating material. The protective film covers at least the concaveportions and the side surfaces of each of the piezoelectric layers ofthe respective piezoelectric elements.

According to the third aspect, it is possible to prevent thepiezoelectric elements from being damaged by moisture and the like inthe air. In addition, the curved inner surface and the curved edge ofthe opening of the concave portion improve the adhesion of theprotective film. This results in a securer prevention of damage to thepiezoelectric elements.

A fourth aspect of the invention provides the actuator device accordingto the third aspect with the protective film provided across theplurality of piezoelectric elements.

According to the fourth aspect, it is possible to prevent thepiezoelectric elements from being damaged by moisture and the like inthe air.

A fifth aspect of the invention provides the actuator device accordingto any one of the first to fourth aspects with the followingcharacteristics. The upper electrodes provided to the respectivepiezoelectric elements are independent of one another. In addition, theend portions of each upper electrode in the shorter-side direction ofeach piezoelectric element define the end portions, in the shorter-sidedirection, of a piezoelectric active portion, which is to be asubstantial driving unit of the corresponding piezoelectric element.Moreover, the end portions of the lower electrode in the longitudinaldirection of each piezoelectric element define the end portions, in thelongitudinal direction, of the piezoelectric active portion.

According to the fifth aspect, the piezoelectric active portion has theend portions in the longitudinal direction defined by the lowerelectrode and the end portions in the shorter-side direction by theupper electrodes. Accordingly, it is possible to achieve high-densitypiezoelectric elements.

A sixth aspect of the invention provides a liquid-jet head that includesan actuator device according to any one of the first to fifth aspects asa liquid-ejecting unit configured to jet a liquid.

According to the sixth aspect, it is possible to improve the drivedurability and, as a consequence, the reliability of the liquid-jethead. In addition, it is also possible to achieve a liquid-jet head withimproved liquid-ejecting characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is an exploded perspective view of a recording head according toEmbodiment 1.

FIG. 2A is a plan view of the recording head according to Embodiment 1.

FIG. 2B is a cross-sectional view of the recording head according toEmbodiment 1.

FIG. 3A is another cross-sectional view of the recording head accordingto Embodiment 1.

FIG. 3B is an enlarged cross-sectional view of a chief part in FIG. 3A.

FIG. 4A is a first cross-sectional view showing a method ofmanufacturing the recording head according to Embodiment 1.

FIG. 4B is a second cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 4C is a third cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 5A is a fourth cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 5B is a fifth cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 5C is a sixth cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 6A is a seventh cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 6B is an eight cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 7A is a ninth cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 7B is a tenth cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

FIG. 8 is an eleventh cross-sectional view showing the method ofmanufacturing the recording head according to Embodiment 1.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the invention will be described in detail.

Embodiment 1

FIG. 1 is an exploded perspective view of an ink-jet recording head thatis an example of a liquid-jet head according to Embodiment 1 of theinvention. FIG. 2A is a plan view of a passage-forming substrate, andFIG. 2B is a cross-sectional view in the longitudinal direction of apressure-generating chamber. FIG. 3A is a cross-sectional view takenalong the line A-A′ in FIG. 2B, and FIG. 3B is an enlargedcross-sectional view of a chief part in FIG. 3A. In this embodiment, asshown in the drawings, a passage-forming substrate 10 is made of asingle-crystal silicon substrate with (110) crystal plane orientation,and an elastic film 50 made of silicon dioxide is formed in advance onone surface of the passage-forming substrate 10 by means of thermaloxidation. Here, the elastic film 50 has a thickness of 0.5 μm to 2 μm.

In the passage-forming substrate 10, a plurality of pressure-generatingchambers 12 are formed by anisotropically etching the passage-formingsubstrate 10 from the other surface of the passage-forming substrate 10.The pressure-generating chambers 12 are partitioned by a plurality ofcompartment walls 11, and are arranged in a row in the width direction(in the direction of the shorter side of each pressure-generatingchamber 12, which is hereinafter referred to as the shorter-sidedirection). In addition, a communicating portion 13 is formed in aregion in the passage-forming substrate 10 on the outer side in thelongitudinal direction of the pressure-generating chambers 12. Inksupply paths 14 are provided respectively to the pressure-generatingchambers 12, and the communicating portion 13 communicates with thepressure-generating chambers 12 respectively through the correspondingink supply paths 14. The communicating portion 13 also communicates witha reservoir portion 31 of a protection plate 30, which is to bedescribed later, so as to form a part of a reservoir 100, which servesas a common liquid chamber for the pressure-generating chambers 12. Eachof the ink supply paths 14 is formed in a width smaller than the widthof each of the pressure-generating chambers 12, so as to maintain, at aconstant level, the passage resistance of ink flowing into each of thepressure-generating chambers 12 from the communicating portion 13.Incidentally, in the embodiment, each ink supply path 14 is formed bynarrowing down the width of a corresponding passage from one side, butit may be formed by narrowing the width from both sides. Moreover, eachink supply path 14 may be formed by narrowing not the width but thethickness of the corresponding passage.

In addition, a nozzle plate 20, with nozzle orifices 21 drilled therein,is fixed to the opening surface side of the passage-forming substrate 10with an adhesive agent, a thermal adhesive film or the like. The nozzleorifices 21 communicate respectively with vicinities of the oppositeends of the pressure-generating chambers 12 to the corresponding inksupply paths 14. It should be noted that the nozzle plate 20 is made of,for example, glass-ceramic materials, a single-crystal siliconsubstrate, stainless steel or the like.

On the other hand, the elastic film 50 having a thickness of, forexample, about 1.0 μm is formed on the opposite surface of thepassage-forming substrate 10 to the nozzle plate 20, as described above.On the elastic film 50, an insulation film 55 having a thickness of, forexample, about 0.4 μm is formed. Moreover, on the insulation film 55, alower electrode film 60 having a thickness of, for example, about 0.2μm, piezoelectric layers 70 each having a thickness of, for example,about 1.0 μm, and upper electrode films 80 each having a thickness of,for example, about 0.05 μm are laminated by means of a process to bedescribed later. The lower electrode film 60, each of the piezoelectriclayers 70 and a corresponding one of the upper electrode films 80constitute one piezoelectric element 300. Here, each of thepiezoelectric elements 300 indicates a portion including the lowerelectrode film 60, one of the piezoelectric layers 70 and acorresponding one of the upper electrode films 80. In general, each ofthe piezoelectric elements 300 is configured in the following manner.One of the electrodes of each piezoelectric element 300 is used as acommon electrode. Then, the other one of the electrodes and thecorresponding one of the piezoelectric layers 70 are patterned for eachof the pressure-generating chambers 12. In a portion constituted of oneof the electrodes and each piezoelectric layer 70, which are patterned,a piezoelectric strain occurs due to application of a voltage betweenthe two electrodes. This portion is hereinafter called a piezoelectricactive portion 320. In the embodiment, the lower electrode film 60 isused as a common electrode for the piezoelectric elements 300, and eachof the upper electrode films 80 is used as an individual electrode forthe corresponding one of the piezoelectric elements 300. However, itdoes not matter even if functions of the two electrode films arereversed due to the conditions of a drive circuit or wirings. In anycase, the piezoelectric active portion 320 is formed for eachpressure-generating chamber 12.

In addition, as shown in FIGS. 2A, 2B, 3A and 3B, in the embodiment, endportions of the lower electrode film 60 in the longitudinal direction ofthe pressure-generating chambers 12 (end portions of the lower electrodefilm 60 in the longitudinal direction of the piezoelectric elements 300)are provided within a region facing the pressure-generating chambers 12.Accordingly, end portions (the length) in the longitudinal direction ofthe piezoelectric active portions 320, which serve as actual drive unitsof the respective piezoelectric elements 300 are defined. Moreover, endportions of each upper electrode film 80 in the shorter-side directionof a corresponding one of the pressure-generating chambers 12 (endportions of each upper electrode film 80 in the shorter-side directionof a corresponding one of the piezoelectric elements 300) are providedwithin a region facing the corresponding one of the pressure-generatingchambers 12. Accordingly, end portions (the width) of each piezoelectricactive portion 320 in the shorter-side direction are defined. In otherwords, each piezoelectric active portion 320 is formed by the lowerelectrode film 60 and the corresponding one of the upper electrode films80 thus patterned, so as to be only within a region facing thecorresponding one of the pressure-generating chambers 12. Furthermore,in the embodiment, as shown in FIG. 3, each of the piezoelectric layers70 and a corresponding one of the upper electrode film 80 are patternedin a manner that the width of the upper electrode film 80 side issmaller than that of the piezoelectric layer 70 side. Accordingly, eachof the piezoelectric layers 70 and the corresponding one of the upperelectrode film 80 have an inclined side surface.

In addition, a device, in which the piezoelectric elements 300 areprovided on a predetermined plate and are driven, is here called anactuator device. In the embodiment, the lower electrode film 60 isprovided along a direction in which the plurality of piezoelectricelements 300 are provided in a row. In addition, in the embodiment, endportions of the lower electrode film 60 in the longitudinal direction ofeach pressure-generating chamber 12 are provided so as to face thepressure-generating chambers 12. Moreover, in the above describedexample, the elastic film 50, the insulation film 55 and the lowerelectrode film 60 function together as a vibration plate. The inventionis not limited to the case of this example. For example, the lowerelectrode film 60 may be configured to function by itself as a vibrationplate without the elastic film 50 and the insulation film 55.

In addition, as shown in FIGS. 3A and 3B, a thin film portion 61 isprovided to a region in the lower electrode film 60 between eachadjacent two of the piezoelectric elements 300. Each thin film portion61 has a thickness smaller than that of a region in the lower electrodefilm 60, which region is to be a part of the piezoelectric element 300.Moreover, a concave portion 62 is provided to the boundary portion inthe lower electrode film 60 between each thin film portion 61 and thepiezoelectric element 300 adjacent thereto. In the lower electrode film60, a region in which the concave portion 62 is formed, is formed in athickness smaller than the thickness of the thin film portion 61. Let'sassume that the thickness of the lower electrode film 60 provided in aregion where each piezoelectric element 300 is provided, is a; thethickness of a region where the thin film portion 61 is provided is b;and the thickness of a region where the concave portion 62 is providedis c. The relationship among the thicknesses satisfies an inequality:a>b>c. In the embodiment, the thickness a of the region that is to be apart of the piezoelectric element 300, of the lower electrode film 60 isset at 200 nm. In addition, the thickness b of the region, where thethin film portion 61 is provided, of the lower electrode film 60 is setat about 180 nm. Moreover, the thickness c of the region, where theconcave portion 62 is provided, of the lower electrode film 60 ispreferably set at 20 nm or more. This is because of the followingreasons. Suppose that, in the lower electrode film 60, the thickness cof the region where the concave portion 62 is provided is smaller than20 nm. In this case, the electrical conductivity between a part of thelower electrode film 60 provided to each piezoelectric element 300 andthe thin film portion 61 of the lower electrode film 60 (a part of thelower electrode film 60 between the two piezoelectric elements 300adjacent to each other) is decreased. In addition, the area of the lowerelectrode film 60 is decreased. Accordingly, when a large number of thepiezoelectric elements 300 are driven at the same time, voltage dropoccurs. As a result, stable ink-ejecting characteristics cannot beachieved. That is, by setting at 20 nm or more the thickness c of theregion, where the concave portion 62 is provided, of the lower electrodefilm 60, the cross-sectional area of the lower electrode film 60 isincreased, and accordingly, the resistance of the lower electrode film60 is decreased. This makes it possible to prevent the occurrence of thevoltage drop when a large number of the piezoelectric elements 300 aredriven at the same time. As a result, stable ink-ejectingcharacteristics can be constantly obtained.

In addition, the concave portions 62 are provided in a manner that theinner surface of each concave portion 62 and the edge of the opening,which is opposite to the adjacent piezoelectric element 300, of eachconcave portion 62 are formed into curved surfaces. Specifically, thecross-sectional shapes of the concave portions 62, in the direction inwhich the piezoelectric elements 300 are provided in a row, of the innersurface of each concave portion 62 and of the edge of the opening, whichis opposite to the adjacent piezoelectric element 300, of the concaveportion 62 are formed into “R” shapes. It is preferable that the radiusof curvature of the inner surface of the concave portion 62 be 50 nm ormore, while it is preferable that the radius of curvature of the edge ofthe opening, which is opposite to the piezoelectric elements 300, of theconcave portion 62 be 50 nm or more.

In this manner, in a region in the lower electrode film 60 between eachadjacent two of the piezoelectric elements 300, the thin film portion 61is provided, which has the thickness smaller than that of a region inthe lower electrode film 60 being a part of the piezoelectric elements300. In addition, the concave portion 62 is provided to the boundaryportion in the lower electrode film 60 between each thin film portion 61and the piezoelectric elements 300 adjacent thereto. This makes itpossible to reduce the thickness c of the lower electrode film 60 on thetwo sides of each piezoelectric element 300 by providing the concaveportions 62. Accordingly, the displacement characteristics of thevibration plate constituted of the lower electrode film 60 is improved,so that the displacement characteristics of the piezoelectric elements300 are improved. As a result, the ink-ejecting characteristics areimproved.

Moreover, in a region in the lower electrode film 60 between eachadjacent two of the piezoelectric elements 300, the thin film portion 61is provided, which has the thickness larger than the thickness c of thepart of the lower electrode film 60 where the concave portion 62 isprovided. Accordingly, it is possible to improve the ink-ejectingcharacteristics, while the reliability is improved by maintaining therigidity of the vibration plate, and by thus maintaining the drivedurability. That is, if the thickness of the region in the lowerelectrode film 60 between each adjacent two of the piezoelectricelements 300 were made equal to the thickness of the region in the lowerelectrode film 60 where the concave portion 62 is provided, the rigidityof the vibration plate should be deteriorated. As a result, when thepiezoelectric elements 300 are repeatedly driven, the vibration platesare damaged.

Furthermore, in the embodiment, the inner surface of each concaveportion 62 and the edge of the opening, which is opposite to theadjacent piezoelectric element 300, of each concave portion 62 areformed into curved surfaces, respectively. Accordingly, the rigidity ofthe region in the lower electrode film 60 where the concave portion 62is provided is improved so that the lower electrode film 60 is preventedfrom being damaged. As a result, it is possible to improve the drivedurability. In addition, by forming the inner surface of the concaveportion 62 into a curved surface, it is possible to improve the rigidityof the vibration plate in the region where the concave portion 62 isprovided. As a result, the drive durability can be more surely improved.

In addition, at least each concave portion 62 and the side surfaces ofthe piezoelectric layer 70 of each piezoelectric element 300 are coveredwith a protective film 200 made of a moisture-resistant insulationmaterial. In the embodiment, the protective film 200 is provided tocover the side surfaces of the piezoelectric layers 70, the sidesurfaces of the upper electrode films 80 and the peripheral edges of theupper surfaces of the upper electrode films 80. Moreover, the protectivefilm 200 is provided to continuously extend across the plurality ofpiezoelectric elements 300. In other words, the protective film 200 isnot provided on a chief part of the upper surface of each upperelectrode film 80, which part is substantially the center region in theupper surface of each upper electrode film 80. Accordingly, openingportions 201 are provided, respectively on the chief parts of the uppersurfaces of the upper electrode films 80, to open the chief parts.

Each opening portion 201 penetrates the protective film 200 in thethickness direction so as to open the protective film 200 in arectangular shape along the longitudinal direction of each piezoelectricelement 300. For example, the opening portions 201 can be formed byselectively patterning the protective film 200 after the protective film200 is formed over the entire surface of the passage-forming substrate10.

By covering the piezoelectric elements 300 with the protective film 200in the above described manner, it is possible to prevent damage to thepiezoelectric elements 300 due to moisture and the like in the air.Here, for the protective film 200, any moisture-resistant material maybe used. For example, it is preferable to use an inorganic insulatingmaterial, such as a silicon oxide (SiO_(x)), a tantalum oxide (TaO_(x))or an aluminum oxide (AlO_(x)). It is especially preferable to use analuminum oxide (AlO_(x)) that is an inorganic amorphous material, forexample, alumina (Al₂O₃). When an aluminum oxide is used as a materialfor the protective film 200, it is possible to sufficiently preventmoisture transmission under a high humidity environment even in a casewhere the film thickness of the protective film 200 is made relativelysmall, for example, about 100 nm. In the embodiment, alumina (Al₂O₃) isused for the protective film 200.

In addition, by providing the opening portions 201 in the protectivefilm 200, it is possible to maintain favorable ink-ejectingcharacteristics without inhibiting the displacements of thepiezoelectric elements 300 (the piezoelectric active portions 320).

Moreover, in the embodiment, the inner surface of each concave portion62 and the edge of the opening, which is opposite to the adjacentpiezoelectric element 300, of the concave portion 62 are formed intocurved surfaces. Accordingly, it is possible to improve the adhesion ofthe protective film 200 on the concave portions 62 and the thin filmportions 61 so as to securely protect the piezoelectric elements 300. Asa result, it is possible to surely prevent the piezoelectric elements300 from being damaged. In other words, a corner existing in the innersurface of the concave portion 62, in the edge of the opening or thelike, brings about a weak adhesion of the protective film 200, whichresults in a formation of the protective film 200 in a step-like shape.When the protective film 200 is formed in a step-like shape in this way,a drive of the piezoelectric element 300 produces a crack in the step.The crack, in turn, leads to damage to the piezoelectric element 300 bymoisture.

On the protective film 200, lead electrodes 90 made of, for example,gold (Au), are provided. One end portion of each lead electrode 90 isconnected to the corresponding upper electrode film 80 via acorresponding one of communicating holes 202 provided in the protectivefilm 200. In addition, the other end portion of each lead electrode 90extends to the side of the ink supply paths 14 in the passage-formingsubstrate 10. The extended other end portions of the lead electrodes 90are connected to a drive circuit 120, to be described later, for drivingthe piezoelectric elements 300 respectively via connecting wirings 121.

Moreover, a protection plate 30 is joined with an adhesive agent 35 tothe top of the passage-forming substrate 10 where the piezoelectricelements 300 are formed. The reservoir portion 31 is formed in a regionfacing the communicating portion 13, in the protection plate 30. Thereservoir portion 31 communicates, as described above, with thecommunicating portion 13 in the passage-forming substrate 10 so as toform a part of the reservoir 100, which serves as the common liquidchamber for the pressure-generating chambers 12.

In addition, a piezoelectric element holding portion 32 is provided in aregion facing the piezoelectric elements 300, in the protection plate30. The piezoelectric element holding portion 32 is configured to haveenough space in a region facing the piezoelectric element 300 to allowan uninhibited movement of the piezoelectric elements 300. It should benoted that, as long as the piezoelectric element holding portion 32 hasenough space so that the movement of the piezoelectric elements 300 isnot inhibited, it does not matter whether or not the space is sealedwith the piezoelectric element holding portion 32.

Moreover, a penetrated hole 33 is provided in a region between thepiezoelectric element holding portion 32 and the reservoir portion 31,in the protection plate 30. The penetrated hole 33 penetrates theprotection plate 30 in the thickness direction. Apart of the lowerelectrode film 60 and the leading end portion of each lead electrode 90are exposed in the penetrated hole 33.

In addition, the drive circuit 120 for driving the piezoelectricelements 300 is mounted on the protection plate 30. As the drive circuit120, it is possible to use, for example, a circuit board, asemiconductor integrated circuit (IC) or the like. The drive circuit 120and each lead electrode 90 are electrically connected to each other viathe connecting wiring 121 formed of a conductive wire, such as a bondingwire.

For the protection plate 30, it is preferable to use a material havingsubstantially the same thermal expansion coefficient as that of thepassage-forming substrate 10, for example, glass, a ceramic material orthe like. In the embodiment, the protection plate 30 is made of asingle-crystal silicon substrate with (110) crystal plane orientation,which is the same material as that of the passage-forming substrate 10.

In addition, a compliance plate 40 is joined to the top of theprotection plate 30. The compliance plate 40 is constituted of a sealingfilm 41 and a fixing plate 42. Here, the sealing film 41 is made of aflexible material with low rigidity (for example, polyphenylene sulfide(PPS) film having a thickness of 6 μm). One side of the reservoirportion 31 is sealed with the sealing film 41. On the other hand, thefixing plate 42 is made of a hard material, such as metal (for example,stainless steel (SUS) or the like having a thickness of 30 μm). Anopening portion 43 is formed in a region facing the reservoir 100 in thefixing plate 42. In the opening portion 43, part of the fixing plate 42is completely removed in the thickness direction. For this reason, oneside of the reservoir 100 is sealed with only the flexible sealing film41.

In the ink-jet recording head of the embodiment as described above, inkis, firstly, taken in from unillustrated external ink supply means, sothat the inside of the ink-jet recording head, from the reservoir 100 tothe nozzle orifices 21, is filled with the ink thus taken in. Then,voltage is applied between the lower electrode film 60 and the upperelectrode films 80, which correspond to the respectivepressure-generating chambers 12 in accordance with recording signalstransmitted from the drive circuit 120. Accordingly, the elastic film50, the insulation film 55, the lower electrode film 60 and thepiezoelectric layers 70 are flexurally deformed so that the pressure ineach pressure-generating chamber 12 is increased. As a result, inkdroplets are ejected from the nozzle orifices 21.

Hereinafter, descriptions will be given of a method of fabricating suchan ink-jet recording head as described above, with reference to FIGS. 4Ato 8. FIGS. 4A to 8 are cross-sectional views, which are taken along adirection in which the pressure-generating chambers are arranged in arow, and which shows the method of fabricating an ink-jet recordinghead.

Firstly, as shown in FIG. 4A, a wafer 110 for a passage-formingsubstrate, which is a silicon wafer formed of a single-crystal siliconsubstrate, is thermally oxidized in a diffusion furnace at a temperatureof about 1100° C. Accordingly, a silicon dioxide film 150, which is toconstitute an elastic film 50, is formed on the surface of the wafer 110for a passage-forming substrate. It should be noted that, in theembodiment, a silicon wafer with (110) priority orientation, which has arelatively large thickness of about 625 μm, and as a result, a highrigidity, is used for the wafer 110 for a passage-forming substrate.

Next, as shown in FIG. 4B, an insulation film 55 made of zirconiumdioxide (ZrO₂) is formed on the elastic film 50 (the silicon dioxidefilm 150). Specifically, a zirconium (Zr) layer is firstly formed on theelastic film 50 by means of a sputtering method or the like. Then, thezirconium layer thus formed is thermally oxidized in a diffusion furnaceat the temperature of, for example, 500° C. to 1200° C., so that theinsulation film 55 made of zirconium dioxide is formed.

Then, as shown in FIG. 4C, a lower electrode film 60 is formed bylaminating, for example, platinum (Pt) and iridium (Ir) on theinsulation film 55. Thereafter, the lower electrode film 60 thus formedis patterned into a predetermined shape. Incidentally, the material forthe lower electrode film 60 is not limited to that formed by laminatingplatinum (Pt) and iridium (Ir), and a material obtained by alloyingplatinum (Pt) with iridium (Ir) may also be used. Any one of platinumand iridium may also be used to form a single layer to function as thelower electrode film 60. Alternatively, it is also possible to use ametal, a metal oxide or the like other than these above-mentionedmaterials.

Subsequently, as shown in FIG. 5A, a piezoelectric layer 70 made oflead-zirconate-titanate (PZT), for example, and an upper electrode film80 made of iridium, for example, are sequentially formed over the entiresurface of the wafer 110 for a passage-forming substrate.

Thereafter, as shown in FIG. 5B, the piezoelectric layer 70 and theupper electrode film 80 thus formed are patterned into a shapecorresponding to regions facing respective pressure-generating chambers12, so that piezoelectric elements 300 are formed. The piezoelectriclayer 70 and the upper electrode film 80 can be patterned at once in thefollowing manner. Specifically, a resist 160 is formed into apredetermined shape on the upper electrode film 80 by means of aphotolithography method. Then, the piezoelectric layer 70 and the upperelectrode film 80 are patterned by dry etching with the resist 160.

In addition, when the piezoelectric layer 70 and the upper electrodefilm 80 are patterned by dry etching, the dry etching is continuouslyperformed until the etched portions reach the lower electrode film 60.By performing this dry etching, the thin film portions 61 and theconcave portions 62 area also provided in the lower electrode film 60.Specifically, each thin film portion 61 having a thickness smaller thanthat of each piezoelectric element 300 is formed in the lower electrodefilm 60 between each adjacent two of the piezoelectric elements 300,while each concave portion 62 is formed in the boundary portion betweeneach thin film portion 61 and the piezoelectric element 300 adjacentthereto. Moreover, at this time, the concave portions 62 are formed in amanner that the inner surface of each concave portion 62 and an edge ofthe opening, which is opposite to the adjacent piezoelectric element300, of the concave portion 62 are formed into curved surfaces.

The thin film portions 61 and the concave portions 62 as described abovecan be consciously formed by appropriately changing the voltage, thetemperature and the like at the time of performing the dry etching. Inaddition, by performing the dry etching on regions each in the lowerelectrode film 60 between each two adjacent piezoelectric elements 300,it is possible to make the surface roughness of the lower electrode film60 uniform. Accordingly, when the protective film 200 is formed on thelower electrode film 60 in a process to be described later, it ispossible to improve the adhesion of the protective film 200.

In the embodiment, the thin film portions 61 and the concave portions 62are formed at one time when the dry etching is performed on thepiezoelectric layer 70 and the upper electrode film 80. However, themethod of forming the thin film portions 61 and the concave portions 62is not limited to this. For example, the thin film portions 61 and theconcave portions 62 may be formed in the following manner. Specifically,when the resist 160 is formed, part of the resist 160 is thinly left inregions other than those in which the concave portions 62 are formed.Accordingly, when the piezoelectric layer 70 and the upper electrodefilm 80 are patterned by dry etching with the resist 160, the thin filmportions 61 and the concave portions 62 are easily formed.

In addition, as a material for the piezoelectric layer 70 constitutingthe piezoelectric elements 300, it is possible to use, for example, aferroelectric-piezoelectric material, such as lead-zirconate-titanate(PZT); or a relaxor ferroelectric, which is obtained by adding a metal,such as niobium, nickel, magnesium, bismuth or yttrium, to theferroelectric-piezoelectric material. The composition of the relaxorferroelectric may be determined in consideration of the characteristics,the usage and the like, of the piezoelectric elements 300. Moreover, themethod of forming the piezoelectric layer 70 is not limited to anyspecific method. For example, in the embodiment, a so-called sol-gelmethod is used for forming the piezoelectric layer 70. Specifically, inthe sol-gel method, sol is obtained by dissolving and dispersing a metalorganic substance in a catalytic agent. The sol is coated and dried soas to be turned into gel. Moreover, the gel is baked at a hightemperature. Consequently, the piezoelectric layer 70 made of a metaloxide is obtained. The method of forming the piezoelectric layer 70 isnot limited to the sol-gel method. Alternatively the piezoelectric layer70 may be formed, for example, by using a method of forming thin films,such as a metal organic decomposition (MOD) method and a sputteringmethod.

In practice, the piezoelectric layer 70 is formed in the followingmanner. A process of forming a piezoelectric film having a smallthickness is repeated a plurality of times by means of the abovedescribed sol-gel method. In this way, the piezoelectric layer 70constituted of a plurality of piezoelectric films thus layered isformed. Moreover, the lower electrode film 60 is formed in the followingmanner. For example, after the lower electrode film 60 is formed abovethe wafer 110 for a passage-forming substrate, a piezoelectric film ofthe first layer is deposited on the lower electrode film 60. Then, thelower electrode film 60 and the piezoelectric film of the first layerare patterned at the same time. This makes it possible to constitute abedding to be used at the time of baking and crystallizing thepiezoelectric film provided above the entire surface of the wafer 110for a passage-forming substrate. As a result, the crystallinity of thepiezoelectric film is improved.

Next, as shown in FIG. 5C, after the resist 160 is removed, theprotective film 200 is formed above the entire surface of the wafer 110for a passage-forming substrate. Thereafter, the protective film 200 ispatterned into a predetermined shape, so that opening portions 201 andcommunicating holes 202 are formed.

Subsequently, as shown in FIG. 6A, lead electrodes 90 made of gold (Au)are formed above the entire surface of the wafer 110 for apassage-forming substrate. Then the lead electrodes 90 are patterned forthe respective piezoelectric elements 300.

Thereafter, as shown in FIG. 6B, a wafer 130 for a protection plate isjoined to the top of the wafer 110 for a passage-forming substrate withthe adhesive agent 35. Here, the reservoir portion 31 and thepiezoelectric element holding portion 32 have been formed in advance inthe wafer 130 for a protection plate. The wafer 130 for a protectionplate is configured to have a thickness of, for example, about 400 μm.For this reason, by joining the wafer 130 for a protection plate to thetop of the wafer 110 for a passage-forming substrate, it is possible tosignificantly improve the rigidity of the wafer 110 for apassage-forming substrate.

Next, as shown in FIG. 7A, the wafer 110 for a passage-forming substrateis polished so as to have a certain thickness. Moreover, wet etching isperformed further on the wafer 110 for a passage-forming substrate byusing a mixture of hydrofluoric-nitric acid as an etchant, so that thewafer 110 for a passage-forming substrate has a predetermined thickness.For example, in the embodiment, by performing the polishing and the wetetching, the wafer 110 for a passage-forming substrate is processed soas to have a thickness of approximately 70 μm.

Subsequently, as shown in FIG. 7B, a mask film 151 made of siliconnitride (SiN) is newly formed on the wafer 110 for a passage-formingsubstrate, and is then patterned into a predetermined shape. Thereafter,anisotropic etching (wet etching) using an alkaline solution, such asKOH, is performed on the wafer 110 for a passage-forming substrate withthe mask film 151 thus patterned. As a result, the pressure-generatingchambers 12, the communicating portions 13 and the ink supply paths 14are formed in the wafer 110 for a passage-forming substrate.

Subsequently, the mask film 151 on the surface of the wafer 110 for apassage-forming substrate, in which surface each pressure-generatingchamber 12 is opened, is removed. Then, unnecessary part of the outerperipheral portions of the wafer 110 for a passage-forming substrate andthe wafer 130 for a protection plate is cut off so as to be removed by,for example, dicing or the like. Subsequently, the nozzle plate 20, inwhich the nozzle orifices 21 are drilled, is joined to the oppositesurface of the wafer 110 for a passage-forming substrate to the wafer130 for a protection plate. At the same time, a compliance plate 40 isjoined to the surface of the wafer 130 for a protection plate.Thereafter, the wafer 110 for a passage-forming substrate and the likeare divided into pieces of passage-forming substrates 10 and the like,each piece having one chip size as shown in FIG. 1. As a result, anink-jet recording head having the above-described configuration isfabricated.

Other Embodiments

Although Embodiment 1 of the invention has been described above, thebasic configuration of the invention is not limited to that describedabove. For example, in Embodiment 1 described above, the protection film200 is provided continuously on the plurality of piezoelectric elements300 (piezoelectric active portion 320). However, the configuration isnot limited to this. For example, the protective film 200 may beprovided individually for each piezoelectric element 300.

Moreover, Embodiment 1 has been described by giving an ink-jet recordinghead as an example of liquid-jet heads. However, the invention isintended to be widely applied to the entire range of liquid-jet heads.The invention can be applied to any liquid-jet head which ejects aliquid other than ink. Examples of liquid-jet head which ejects a liquidother than ink include: various recording heads used for image recordingapparatuses such as printers; heads that eject liquids containing colormaterials used for manufacturing color filters of liquid crystal displaydevices and the like; electrode-material-jet heads used for formingelectrodes of organic EL display devices, FED (Field Emission Display)devices and the like; bio-organic-substance-jet heads used formanufacturing bio-chips; and the like. It should be noted that theinvention can be applied to not only actuator devices to be mounted onliquid-jet heads (ink-jet recording head and the like), but alsoactuator devices to be mounted on any kinds of apparatuses.

1. An actuator device comprising: a plurality of piezoelectric elementsformed on a surface of a substrate, each piezoelectric element beingconfigured of a piezoelectric layer, an upper electrode, and a lowerelectrode that is formed across the plurality of piezoelectric elements;a thin film portion provided to a region in the lower electrode betweeneach adjacent two of the piezoelectric elements, the thin film portionhaving a thickness smaller than that of a region in the lower electrodeprovided to each piezoelectric element; and a concave portion providedto the boundary portion between each thin film portion and thepiezoelectric element adjacent thereto, wherein the inner surface and anedge of the opening, which is opposite to the adjacent piezoelectricelement, of the concave portion are formed into curved surfaces.
 2. Theactuator device according to claim 1 wherein the thin film portion andthe concave portion are provided along the longitudinal direction ofeach piezoelectric element.
 3. The actuator device according to claim 1further comprising a protective film formed of an insulating material,the protective film covering at least the concave portions and the sidesurfaces of each piezoelectric layer of each piezoelectric element. 4.The actuator device according to claim 3 wherein the protective film isprovided across the plurality of piezoelectric elements.
 5. The actuatordevice according to claim 1 wherein the upper electrodes provided to therespective piezoelectric elements are independent of one another, theend portions of each upper electrode in the shorter-side direction ofeach piezoelectric element define the end portions, in the shorter-sidedirection, of a piezoelectric active portion, which is to be asubstantial driving unit of the corresponding piezoelectric element, andthe end portions of the lower electrode in the longitudinal direction ofeach piezoelectric element define the end portions of the piezoelectricactive portion in the longitudinal direction.
 6. A liquid-jet headcomprising an actuator device according to claim 1 as a liquid-ejectingunit configured to jet a liquid.